This invention is directed to a system for adjusting the target with respect to the optics in a focused beam system to place the active surface of the target at the proper point.
When optics focus a beam at a target there may be changes in the system which cause the optimum focal point not to be at the effective surface of the target. For example, if the target is a series of similar devices, the target thickness may differ so that the effective top surface of the target would be at a different position. Of course the optics can be adjusted so that the focal point appears at the surface of the target but in many optical systems the adjustment of the focal length is quite difficult. Such is particularly true in focused electron beam and ion beam systems. Such beams are used for various purposes, including writing patterns on the target or writing patterns on an etch resist material on the target. For such beams, quite often the target is a semiconductor wafer.